9. Dark Dynasty (Season 10, Episode 21)
The first of many season 10 episodes on this list, Dark Dynasty is a particularly controversial episode due to the death of a fan-favorite character, Charlie. Charlie was one of the first openly gay characters in Supernatural, which made her death receive so much backlash from the fandom.
The problem here is how unnecessary her death felt, feeling more like a product of lazy writing rather than something that actually contributed to the plot. Killing a beloved character just for the shock value is bound to piss off many of the fans of your show and get your episode on the "Most Hated Episodes" list.
Beyond her death, Dark Dynasty features the same formula the show has had for several episodes at that point, making the episode still terrible even if Charlie hadn't died. Many of the fans had wondered at this point if the show was even worth following anymore given how repetitive and formulaic each episode has been. With Dark Dynasty, it became clear that the show had officially jumped the shark.